Method of manufacturing semiconductor device having multi-height structure

ABSTRACT

A method for manufacturing a semiconductor device having a multi-height structure is provided. The semiconductor device having a multi-height structure includes a silicon substrate. A first structure and a second structure are respectively formed on the silicon substrate and connected to each other. A limiting block is formed on the second structure and near an edge of the second structure beside the first structure. A bottom anti-reflection coating (BARC) layer is formed to blanketly cover the first structure, the second structure and the limiting block, in which the BARC layer includes a low-viscosity material, and the BARC layer overlying the top surface of the second structure has an external surface substantially parallel to the top surface of the second structure. Control gates are formed on the external surface of the BARC layer.

RELATED APPLICATIONS

This application is a continuation of U.S. Non-provisional patent application Ser. No. 15/456,820 filed on Mar. 13, 2017, now U.S. Pat. No. 10,211,214 issued on Feb. 19, 2019, which is herein incorporated by reference.

BACKGROUND

Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. It is used in a wide variety of commercial and military electronic devices and equipment. To store information, flash memory includes an addressable array of memory cells, typically made from floating gate transistors. Common types of flash memory cells include stacked gate memory cells and split gate flash memory cells. Split gate flash memory cells are semiconductor devices, typically formed as part of integrated circuits. Recently, split gate flash memory cells have received great attention due to the development of high memory capacities (relative to other types of flash memory cells). Split gate flash memory cells have several advantages over stacked gate memory cells, such as lower power consumption, higher injection efficiency, less susceptibility to short channel effects, and over erase immunity.

However, when a bottom anti-reflection coating (BARC) layer includes a low-viscosity material, the BARC layer has a thinner thickness near an edge of a functional area. An external surface of the BARC layer overlying various features shows a steep slope from a central portion to the edge of the functional area, so that the external surface cannot be parallel to the top surface of the underlying features along a horizontal dot-line. The uneven thickness of the BARC layer causes the overlying control gates near the edge of the functional area to slide down, resulting in worse critical dimension uniformity (CDU) within the functional area.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A and FIG. 1B are schematic cross-sectional views of a semiconductor device having a multi-height structure in accordance with various embodiments.

FIGS. 2A to 2I are schematic cross-sectional views of intermediate stages showing a method of fabricating a semiconductor device having a multi-height structure in accordance with various embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact.

Terms used herein are only used to describe the specific embodiments, which are not used to limit the claims appended herewith. For example, unless limited otherwise, the term “one” or “the” of the single form may also represent the plural form. The terms such as “first” and “second” are used for describing various devices, areas and layers, etc., though such terms are only used for distinguishing one device, one area or one layer from another device, another area or another layer. Therefore, the first area can also be referred to as the second area without departing from the spirit of the claimed subject matter, and the others are deduced by analogy. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Embodiments of the present disclosure are directed to a semiconductor device having a multi-height structure including a first structure having a first height and a second structure having a second height greater than the first height, in which a limiting block acts as a retaining wall to hold or restrain more BARC layer on the second structure, thereby preventing the BARC layer flowing down from a top surface of the second structure.

In some embodiments, as shown in FIG. 1A, which is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with various embodiments.

Briefly, in FIG. 1A, a semiconductor device 100 may include a silicon substrate 101. A first structure 107 and a second structure 109 are respectively disposed on the silicon substrate 101 and connected to each other. A limiting block 125 is disposed on an edge 121 d of a top surface 121 c of the second structure 109 beside the first structure 107. A bottom anti-reflection coating (BARC) layer 135 blanketly covers the first structure 107, the second structure 109 and the limiting block 125. Control gates 141 a, 141 b, 141 c and 141 d are disposed on an external surface 137 of the BARC layer 135.

As shown in FIG. 1A, in certain embodiments, the silicon substrate 101 may be defined into two functional areas including a first functional area 103 and a second functional area 105, in which the first functional area 103 may be defined as a logic cell area, and the second functional area 105 may be defined as a flash cell area, for examples. However, in other embodiments, the first functional area 103 and the second functional area 105 may be other functional areas rather than the aforementioned definitions. In those embodiments, depending actual requirements, the silicon substrate 101 may include structures such as shallow trench isolations (STIs; not shown in the figures) to define areas for active devices, sometimes referred as OD areas (not shown in the figures).

As shown in FIG. 1A, in some embodiments, the first structure 107 may be disposed on the silicon substrate 101. In certain embodiments, the first structure 107 may include a low-gate polysilicon layer 123 disposed above the first functional area 103 of the silicon substrate 101. In these embodiments, the first structure 107 may have a first height H₁ from an upper surface 102 of the silicon substrate 101 to a top surface (not shown in the figures) of the low-gate polysilicon layer 123.

As shown in FIG. 1A, in some embodiments, the second structure 109 may be disposed on the silicon substrate 101 and adjacent to the first structure 107. In certain embodiments, the second structure 109 may include a floating gate polysilicon layer 111 disposed on the silicon substrate 101, and a high-voltage polysilicon layer 121 disposed on the floating gate polysilicon layer 111. In some examples, a dielectric layer 113 may be optionally disposed between the high-voltage polysilicon 121 and the floating gate polysilicon layer 111. The high-voltage polysilicon layer 121 may have a first portion 121 a disposed on the floating gate polysilicon layer 111.

In certain embodiments, the high-voltage polysilicon layer 121 may further have a second portion 121 b, in which the second portion 121 b of the high-voltage polysilicon layer 121 may be optionally extended along the upper surface 102 of the silicon substrate 101 and connected to the low-gate polysilicon layer 123. In these embodiments, the first structure 107 may optionally include the low-gate polysilicon layer 123 and the second portion 121 b of the high-voltage polysilicon layer 121 disposed on the upper surface 102 of the silicon substrate 101.

In those embodiments, the floating gate polysilicon layer 111, the high-voltage polysilicon layer 121 and the low-gate polysilicon layer 123 may include a polysilicon material doped with common concentrations of various known impurities. In these embodiments, the second structure 109 may have a second height H₂ from the upper surface 102 of the silicon substrate 101 to a top surface (high-voltage polysilicon layer 121, and the second height H₂ is greater than the first height H₁. For example, a difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂-H₁)/H₁, may be greater than 3% and is greater than 10% in certain examples.

As shown in FIG. 1A, in some embodiments, the second structure 109 may include a limiting block 125 disposed on the top surface 121 c of the high-voltage polysilicon layer 121 of the second structure 109 near an edge 121 d of the second structure 109 beside the first structure 107. In certain embodiments, the limiting block 125 and the low-gate polysilicon layer 123 may be formed from the same material. In other embodiments, the limiting block 125 and the low-gate polysilicon layer 123 may be defined by the same reticle in the same step or by different reticles in different steps, depending on actual design requirements.

As shown in FIG. 1A, in some embodiments, a bottom anti-reflection coating (BARC) layer 135 may blanketly covers the first structure 107, the second structure 109 and the limiting block 125. In these embodiments, in which the BARC layer 135 in liquid state may include a low-viscosity material having a viscosity of no more than 5000 centipoise (cp), for example. It is noted that cp is an abbreviation of centipoise, 1 P=1 g·s⁻¹·cm⁻¹, viscosity unit: Pa·s=kg·m⁻¹s⁻¹, therefore 1 Pa·s=10 P=1000 cP.

It is noted that, the limiting block 125 acts as a retaining wall to hold or restrain more of the BARC layer 135 on the top surface 121 c and near the edge 121 d of the second structure 109, for preventing the BARC layer 135 flowing down from the top surface 121 c of the second structure 109. It keeps an external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 to be substantially parallel to the top surface 121 c of the second structure 109 along a horizontal dot line 139. That is to say, the BARC layer 135 has a substantially uniform thickness T above the top surface 121 c as shown in FIG. 1A. Accordingly, the limiting block 125 may properly adjust the slope of the external surface 137 of the BARC layer 135 on the top surface 121 c of the second structure 109. In certain examples, the limiting block 125 may decrease the slope of the external surface 137 of the BARC layer 135 approximately to zero on the top surface 121 c of the second structure 109.

In some certain embodiments, the height of the limiting block 125 depends upon the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂-H₁)/ H₁, rather than limiting the height of the limiting block 125. It is noted that, when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂-H₁)/H₁, is greater than 10% in certain examples, the limiting block 125 has a height greater than another limiting block 125 when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂-H₁)/H₁, is greater than 10%. So that the limiting block 125 may hold or restrain much more of the BARC layer 135 on the top surface 121 c and near the edge 121 d of the second structure 109, for enhancing the prevention of the BARC layer 135 flowing down from the top surface 121 c of the second structure 109.

As shown in FIG. 1A, in some embodiments, control gates 141 a, 141 b, 141 c and 141 d may be disposed on the external surface 137 of the BARC layer 135. Since the external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 is extended along the horizontal dot-line 139 substantially parallel to the top surface 121 c of the second structure 109, there is no or little differences in height of the control gates 141 a, 141 b, 141 c and 141 d. That is to say, the BARC layer 135 has a substantially uniform thickness T above the top surface 121 c.

Referring to FIG. 1A, in other embodiments, other material layers maybe optionally disposed below the BARC layer 135 and above the first structure 107, the second structure 109 and the limiting block 125. In certain embodiments, an anti-reflection dielectric (ARD) layer 131 may be optionally disposed to blanketly cover the first structure 107, the second structure 109 and the limiting block 125. In certain embodiments, a passivation layer 133 may be optionally disposed to blanketly cover the ARD layer 131, in which the passivation layer 133 includes silicon oxynitride (SiON).

In other embodiments, the limiting block 125 may be combined with various structures, for effectively preventing the BARC layer 135 flowing down from the top surface 121 c of the second structure 109, and keeping an external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 to be substantially parallel to the top surface 121 c of the second structure 109.

Referring to FIG. 1B. FIG. 1B is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with other embodiments. In other embodiments, as shown in FIG. 1B, the high-voltage polysilicon layer 121 of the second structure 109 may have a first portion 121 a, in which the first portion 121 a may be disposed on the floating gate polysilicon layer 111, and the first portion 121 a may optionally have an opening 122 for exposing a portion of the dielectric layer 113. In these embodiments, a portion of the limiting block 125 may be disposed on the top surface 121 c of the high-voltage polysilicon layer 121 of the second structure 109 near an edge 121 d of the second structure 109 beside the first structure 107, and another portion of the limiting block 125 may extend into the opening 122. The another portion of the limiting block 125 may fill or partially fill the opening 122. The limiting block 125 acts as a retaining wall, and the opening 122 may receive a portion of the ARD layer 131 or a portion of the BARC layer 135 if the ARD layer 131 and passivation layer 133 are not disposed. The limiting block 125 and the opening 122 also may hold or restrain the BARC layer 135 on the top surface 121 c and near the edge 121 d of the second structure 109, for keeping the external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 to be substantially parallel to the top surface 121 c of the second structure 109 along a horizontal dot line 139. That is to say, the BARC layer 135 has a substantially uniform thickness T above the top surface 121 c as shown in FIG. 1A. Accordingly, the limiting block 125 and the opening 122 also may freely adjust the slope of the external surface 137 of the BARC layer 135 on the top surface 121 c of the second structure 109. In certain examples, the limiting block 125 and the opening 122 may decrease the slope of the external surface 137 of the BARC layer 135 on the top surface 121 c of the second structure 109.

The semiconductor devices 100 of FIGS. 1A and 1B can be manufactured as follows. FIG. 2A to FIG. 21 are schematic cross-sectional views of intermediate stages showing a method of fabricating a semiconductor device 200 having a multi-height structure in accordance with various embodiments.

In some embodiments, as shown in FIG. 2A, the semiconductor device 200 may include a silicon substrate 201. In certain embodiments, the silicon substrate 201 may be defined into two areas, a first functional area 203 and a second functional area 205. In those embodiments, the first functional area 203 may be defined as a logic cell area, and the second functional area 205 may be defined as a flash cell area. In those embodiments, the silicon substrate 201 may include structures such as shallow trench isolations (STIs) (not shown in the figures) to define areas for active devices, sometimes referred as OD areas (not shown in the figures).

In some embodiments, as shown in FIG. 2B, the semiconductor device 200 may include a low-gate polysilicon layer (a floating gate polysilicon layer) 211 above an upper surface 202 of a silicon substrate 201 within the second functional area 205. In certain embodiments, the low-gate polysilicon layer 211 may be made from polysilicon or other appropriate conducting materials, which may be formed by a typical process, such as chemical vapor deposition (CVD) process.

In some embodiments, as shown in FIG. 2C, a dielectric layer 213 may be optionally formed on the floating gate polysilicon layer 211.

In some embodiments, as shown in FIG. 2D, a high-voltage polysilicon layer 221 may be formed on the dielectric layer 213 and the floating gate polysilicon layer 211. In certain embodiments, the high-voltage polysilicon layer 221 may have a first portion 221 a formed on the floating gate polysilicon layer 211, a second portion 221 b optionally extending along the upper surface 202 of the silicon substrate 201.

In some embodiments, as shown in FIG. 2E, a low-gate polysilicon layer 223 may be formed the upper surface 202 of the silicon substrate 201 within the first functional area 203 and connected to the second portion 221 b of the high-voltage polysilicon layer 221. Simultaneously, a limiting block 225 may be formed on a top surface 221 c of the high-voltage polysilicon layer 221 and near an edge 221 d thereof beside the low-gate polysilicon layer 223. For saving the processing steps, in some embodiments, the limiting block 225 and the low-gate polysilicon layer 223 may be defined by the same reticle in the same processing step or by different reticles in different processing steps.

In certain embodiments, the low-gate polysilicon layer 223 and the second portion 221 b of the high-voltage polysilicon layer 221 may be defined as a first structure 207. The first portion 221 a of the high-voltage polysilicon layer 221, the low-gate polysilicon layer 211 and optionally the dielectric layer 213 may be defined as a second structure 209.

In some embodiments, as shown in FIG. 2F, an ARD layer 231 may optionally blanketly cover the first structure 207, the limiting block 225 and the second structure 209. Then, a passivation layer 233, including silicon oxynitride (SiON), may optionally blanketly cover the ARD layer 231. Alternatively, in the case of FIG. 21, an opening 222 may be optionally formed in the first portion 221 a of the high-voltage polysilicon layer 221 for exposing a portion of the dielectric layer 213. In these embodiments, a portion of the limiting block 225 may be disposed on the top surface 221 c of the high-voltage polysilicon layer 221 of the second structure 209 near an edge 221 d of the second structure 209 beside the first structure 207, and another portion of the limiting block 225 may extend into the opening 222, for fulfilling the opening 222 or partially.

In some embodiments, as shown in FIG. 2G, a BARC layer 235 may blanketly cover the passivation layer 233. In some embodiments, the BARC layer 235 in liquid phase may include a low-viscosity material having a viscosity smaller than or equal to 5000 centipoise (cp), for example. The BARC layer 235 may be applied on the passivation layer 233 by a typical spin coating process. It is noted that cp is an abbreviation of centipoise, 1 P=1 g·s⁻¹·cm⁻¹, viscosity unit: Pa·s=kg·m⁻¹s⁻¹, therefore 1 Pa·s=10 P=1000 cP.

It is noted that, the limiting block 225, acting as a retaining wall, may be used to hold or restrain more of the BARC layer 235 on the top surface 221 c and near the edge 221 d of the second structure 209, for preventing the BARC layer 235 flowing down from the top surface 221 c of the second structure 209. It keeps an external surface 237 of the BARC layer 235 overlying the top surface 221 c of the second structure 209 to be substantially parallel to the top surface 221 c of the second structure 209 along a horizontal dot line 239. That is to say, the limiting block 225 has a substantially uniform thickness T above the top surface 221 c and appropriately adjusts the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209. In certain examples, the limiting block 225 may decrease the slope of the external surface 237 of the BARC layer 235 approximately to zero on the top surface 221 c of the second structure 209.

In some embodiments, as shown in FIG. 2H, control gates 241 a, 241 b, 241 c and 241 d may be disposed on the external surface 237 of the BARC layer 235 at substantially the same horizontal level.

In some examples, a difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂-H₁)/H₁, is greater than 3%, and is greater than 10% in certain examples. The standard derivation in height of all control gates of the semiconductor device 200 may have a mean of less than 2.6 and a standard derivation of less than 0.26 when the semiconductor device 200 has the limiting block 225 and/or the opening 222. In certain examples, the standard derivation in height of all control gates of the semiconductor device 200 may have a mean of less than 2.4 and a standard derivation of less than 0.20 when the semiconductor device 200 has the limiting block 225 and/or the opening 222. In other certain examples, the standard derivation in height of all control gates of the semiconductor device 200 may have a mean of less than 2.2 and a standard derivation of less than 0.16 when the semiconductor device 200 has the limiting block 225 and/or the opening 222 (data not shown in the figures). The semiconductor device 200 of FIGS. 2H and 21 may have improved (i.e. larger) CD near the edge 221 d of the second functional area 205 (for example, the flash cell area).

Referring to FIG. 21. FIG. 21 is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with other embodiments. In other embodiments, as shown in FIG. 21, the high-voltage polysilicon layer 221 of the second structure 209 may have a first portion 221 a, in which the first portion 221 a may be disposed on the floating gate polysilicon layer 211, and the first portion 221 a may optionally have an opening 222 for exposing a portion of the dielectric layer 213. In these embodiments, a portion of the limit block 225 may be disposed on the top surface 221 c of the high-voltage polysilicon layer 221 of the second structure 209 near an edge 221 d of the second structure 209 beside the first structure 207, and another portion of the limit block 225 may extend into the opening 222. The another portion of the limit block 225 may be filled into the opening 222 or not. The limit block 225 is like a retaining wall, and the opening 222 may receive a portion of the BARC layer 235. The limit block 225 and the opening 222 also may hold or restrain the BARC layer 235 on the top surface 221 c of the second structure 209, for keeping the external surface 237 of the BARC layer 235 overlying the top surface 221 c of the second structure 209 to be substantially parallel to the top surface 221 c of the second structure 209 along a horizontal dot line 239. Accordingly, the limit block 225 and the opening 222 also may freely adjust the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209. In certain examples, the limit block 225 and the opening 222 may decrease the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209.

In comparison with the typical semiconductor device without the limiting block and/or the opening, when a BARC layer includes a low-viscosity material, an external surface of the BARC layer overlying various features shows a steep slope from a central portion to the edge of a functional area, the BARC layer is unlikely held or restrained on the top surface of the underlying various features. Moreover, for example, the BARC layer overlying the top surface of the underlying various features within a functional area has a mean of more than 2.6 and a standard derivation of more than 0.26, and the critical dimension uniformity (CDU) of the semiconductor device within the functional area become worse, leading smaller CD at the edge of the underlying various features (for example, the flash cell area). However, the semiconductor device 200 having the limiting block 225 (e.g. FIG. 2H) and/or the opening 222 within the second functional area 205 (e.g. FIG. 21) may improve approximately 25% CDU in comparison with the semiconductor device within the functional area.

In accordance with an embodiment, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a silicon substrate, a first structure, a second structure, a bottom anti-reflection coating (BARC) layer and control gates. The first structure may be disposed on the silicon substrate, in which the first structure has a first height from an upper surface of the silicon substrate. The second structure may be disposed on the silicon substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the silicon substrate, and the second structure may include a limiting block disposed on a top surface of the second structure near an edge of the second structure beside the first structure. The bottom anti-reflection coating (BARC) layer may cover the first structure, the second structure and the limiting block, in which the BARC layer may include a low-viscosity material, and the BARC layer overlying the top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

In accordance with another embodiment, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a first structure, a second structure, an anti-reflection dielectric (ARD) layer, a BARC layer and control gates. The first structure may be disposed on a silicon substrate, in which the first structure may have a first height from an upper surface of the silicon substrate. The second structure may be disposed on the silicon substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the silicon substrate, and the second structure may include a limiting block disposed on a top surface of the second structure near an edge of the second structure beside the first structure. The ARD layer may cover the first structure, the second structure and the limiting block. The BARC layer may cover the ARD layer, in which the BARC layer may include a low-viscosity material, and the BARC layer above the top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

In accordance with yet another embodiment, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a first structure, a second structure, an ARD layer, a passivation layer, a BARC layer and control gates. The first structure may be disposed on the silicon substrate, in which the first structure may have a first height from an upper surface of the silicon substrate. The second structure may be disposed on the silicon substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the silicon substrate, and the second structure may include a limiting block disposed on a top surface of the second structure near an edge of the second structure beside the first structure. The ARD layer may cover the first structure, the second structure and the limiting block. The passivation layer may cover the ARD layer, in which the passivation layer may include silicon oxynitride (SiON). The BARC layer may cover the passivation layer, in which the BARC layer may include a low-viscosity material, and the BARC layer above the top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

In accordance with yet another embodiment, the present disclosure discloses a method for manufacturing a semiconductor device. In the method, a first gate layer and a dielectric layer are formed over a first functional area of a semiconductor substrate, in which the semiconductor substrate has the first functional area and a second functional area. A second gate layer is formed over the dielectric layer, in which the second gate layer has a first portion over the dielectric layer and a second portion over the semiconductor substrate. A third gate layer is formed over the second functional area of the semiconductor substrate, and a limiting block is formed over the first portion of the second gate layer. A bottom anti-reflection coating (BARC) layer is formed over the third gate layer, the second gate layer, and the limiting block, in which a portion of the BARC layer is restrained over the first functional area by the limiting block.

In accordance with yet another embodiment, the present disclosure discloses a method for manufacturing a semiconductor device. In the method, a first gate layer and a dielectric layer are formed over a first functional area of a semiconductor substrate, in which the semiconductor substrate has the first functional area and a second functional area. A second gate layer is formed over the dielectric layer. A third gate layer is deposited over the second gate layer and the second functional area of the semiconductor substrate. The third gate layer is patterned to form a logic gate layer over the second functional area of the semiconductor substrate and a limiting block over the second gate layer, in which the limiting block is directly over the first gate layer a bottom anti-reflection coating (BARC) layer is formed over the logic gate layer, the second gate layer, and the limiting block, in which a portion of the BARC layer is restrained over the first functional area by the limiting block.

In accordance with yet another embodiment, the present disclosure discloses a method for manufacturing a semiconductor device. In the method, a first gate layer and a dielectric layer are formed over a first functional area of a semiconductor substrate, in which the semiconductor substrate has the first functional area and a second functional area. A second gate layer is formed over the dielectric layer. A third gate layer is formed over the second functional area of the semiconductor substrate and forming a limiting block over the second gate layer, in which a top surface of the limiting block is higher than a topmost surface of the second gate layer. A bottom anti-reflection coating (BARC) layer is formed over the third gate layer, the second gate layer, and the limiting block, in which a portion of the BARC layer is restrained over the first functional area by the limiting block.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method, comprising: forming a first gate layer and a dielectric layer over a first functional area of a semiconductor substrate, wherein the semiconductor substrate has the first functional area and a second functional area; forming a second gate layer over the dielectric layer, wherein the second gate layer has a first portion over the dielectric layer and a second portion over the semiconductor substrate; forming a third gate layer over the second functional area of the semiconductor substrate and forming a limiting block over the first portion of the second gate layer; and forming a bottom anti-reflection coating (BARC) layer over the third gate layer, the second gate layer, and the limiting block, wherein a portion of the BARC layer is restrained over the first functional area by the limiting block.
 2. The method of claim 1, wherein forming the limiting block and forming the third gate layer are performed by using the same reticle.
 3. The method of claim 1, wherein the limiting block and the third gate layer are made of the same material.
 4. The method of claim 1, wherein forming the second gate layer is performed such that a top surface of the first portion of the second gate layer is higher than a top surface of the second portion of the second gate layer.
 5. The method of claim 1, wherein forming the third gate layer is performed such that the second portion of the second gate layer is interposed between the first gate layer and the third gate layer.
 6. The method of claim 1, wherein forming the limiting block is performed such that a bottom surface of the limiting block is higher than a top surface of the second portion of the second gate layer.
 7. The method of claim 1, further comprising: forming an opening in the first portion of the second gate layer to expose a portion of the dielectric layer prior to forming the limiting block.
 8. The method of claim 7, wherein forming the limiting block is performed such that the limiting block extends into the opening.
 9. The method of claim 1, further comprising: forming an anti-reflection dielectric (ARD) layer over the third gate layer, the second gate layer, and the limiting block prior to forming the BARC layer.
 10. The method of claim 9, further comprising: forming a passivation layer over the ARD layer prior to forming the BARC layer.
 11. A method, comprising: forming a first gate layer and a dielectric layer over a first functional area of a semiconductor substrate, wherein the semiconductor substrate has the first functional area and a second functional area; forming a second gate layer over the dielectric layer; forming a third gate layer over the second gate layer and the second functional area of the semiconductor substrate; patterning the third gate layer to form a logic gate layer over the second functional area of the semiconductor substrate and a limiting block over the second gate layer, wherein the limiting block is directly over the first gate layer; and forming a bottom anti-reflection coating (BARC) layer over the logic gate layer, the second gate layer, and the limiting block, wherein a portion of the BARC layer is restrained over the first functional area by the limiting block.
 12. The method of claim 11, further comprising: forming an opening in the second gate layer to expose a portion of the dielectric layer; and forming an anti-reflection dielectric (ARD) layer over the second gate layer, such that the ARD layer extends into the opening.
 13. The method of claim 12, wherein patterning the third gate layer is performed such that the limiting block lands over the exposed portion of the dielectric layer.
 14. The method of claim 11, wherein patterning the third gate layer is performed such that the limiting block is directly over the dielectric layer.
 15. The method of claim 11, further comprising: forming an anti-reflection dielectric (ARD) layer over the second gate layer and the limiting block prior to forming the BARC layer, such that the ARD layer has a raised portion over the limiting block.
 16. The method of claim 15, further comprising: forming a passivation layer over the ARD layer prior to forming the BARC layer, such that the passivation layer has a raised portion over the limiting block.
 17. The method of claim 16, wherein forming the BARC layer is performed such that the BARC layer has a raised portion over the limiting block.
 18. A method, comprising: forming a first gate layer and a dielectric layer over a first functional area of a semiconductor substrate, wherein the semiconductor substrate has the first functional area and a second functional area; forming a second gate layer over the dielectric layer; forming a third gate layer over the second functional area of the semiconductor substrate and forming a limiting block over the second gate layer, wherein a topmost surface of the limiting block is higher than a topmost surface of the second gate layer; and forming a bottom anti-reflection coating (BARC) layer over the third gate layer, the second gate layer, and the limiting block, wherein a portion of the BARC layer is restrained over the first functional area by the limiting block.
 19. The method of claim 18, wherein the limiting block comprises polysilicon.
 20. The method of claim 18, wherein forming the limiting block is performed such that a bottom surface of the limiting block is higher than a top surface of the third gate layer. 